Electric heater for use in a duct work system

ABSTRACT

A heater adapted for use in a duct work system includes a unitary assembly of (1) a housing unit supporting at least one resistance wire heating element having a pair of terminals, (2) a control box containing heating element controls attached to and positioned outside the housing unit and (3) an enclosed terminal box housing the terminals and the electrical connections between the terminals and the controls in the control box. The terminal box is disposed adjacent the control box and positioned within the housing unit. The housing unit, terminal box and control box are so dimensioned relative to the duct work that when the heater is installed within the duct work both the housing unit and terminal box are recessed within the duct work in the path of the airstream while the control box is outside the duct work. The terminal box also contains thermal cutouts connected to the heating element. The space heater can be of the &#39;&#39;&#39;&#39;slip-in&#39;&#39;&#39;&#39; or &#39;&#39;&#39;&#39;flange&#39;&#39;&#39;&#39; type.

United States atet [72] Inventor Jerome F. Brasch 1 1327 Clayton Road, St. Louis, Mo. 63131 [21] Appl. No. 879,412 [22] Filed Nov. 24, 1969 [45] Patented Dec. 28, 1971 [54] ELECTRIC HEATER FOR USE IN A DUCT WORK SYSTEM 3 Claims, 7 Drawing Figs.

[52] U.S. Cl 219/366, 219/364, 219/374, 219/375, 219/381, 219/532 [51] Int. Cl F24h 3/04, H051) 1/00 [50] Field of Search 219/363, 364, 365-370, 374-377, 380, 381, 382, 532, 536

[56] References Cited UNITED STATES PATENTS 1,217,229 2/1917 Smith 219/364 2,712,588 7/1955 Epstein. 219/374 2,893,639 7/1959 Martin..... 219/375 X 3,098,145 7/1963 Raymond... 219/374X 3,102,185 8/1963 Boyd et a1 219/374X Primary Examiner-A. Bartis AttorneySidney B. Ring ABSTRACT: A heater adapted for use in a duct work system includes a unitary assembly of (1) a housing unit supporting at least one resistance wire heating element having a pair of terminals, (2) a control box containing heating element controls attached to and positioned outside the housing unit and (3) an enclosed terminal box housing the terminals and the electrical connections between the terminals and the controls in the control box. The terminal box is disposed adjacent the control box and positioned within the housing unit. The housing unit, terminal box and control box are so dimensioned relative to the duct work that when the heater is installed within the duct work both the housing unit and terminal box are recessed within the duct work in the path of the airstream while the control box is outside the duct work. The terminal box also contains thermal cutouts connected to the heating element. The space heater can be of the slip-in or flange" type.

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THERMAL CONTROL BOX INVEN 752 524s! 3.4%. may 7 ELECTRIC HEATER FOR USE IN A DUCT WORK SYSTEM This invention relates to improvements in an electrical heating apparatus and has particular reference to improvements in a resistance wire heater which is installed in and forms part of a forced-air heating system.

In recent years forced-air heating has become quite popular. Its use has been accelerated by the fact that an air-conditioning system can also use the same ducts as the forced-air heating system. Furthermore, with the advent of low-cost electricity and better engineering and insulation, the use of forcedair electric heat has become increasingly popular. The simplicity of the design and use of resistance electric heating units plus the fact that they can be installed economically in a plurality of places in the duct system with individual unit controls has accelerated the trend. The simplicity of their installation is illustrated in FIGS. 1 and 2 where FIG. 1 shows the installation of a slip-in" unit in a forced-air duct heating system and FIG. 2 illustrates joining of flanges" of the heater with two flanged ducts to yield an easily installed heating apparatus joined to the ducts.

Heretofore, electrical heating apparatus employed in ducts of forced-air heating systems have had their resistance coil terminals positioned in the control box which is installed outside of the air ducts. A prior art electrical heating apparatus is illustrated in US. Pat. No. 2,712,588. In certain instances as (I) where the resistance coil terminals are blocked by duct insulation, (2) where the heater has obstructions from components installed in the duct or air-handling system, or (3) where the heater is installed in a location having inadequate airflow near the tenninal box as, for example, where the heater is mounted close to a bend in the duct work and the control box is located on the inside wall of the bend, etc., the flow of air, which is vital to proper operation, is blocked thus allowing the terminals to build up excessive heat. When this occurs the heater may continually cycle when overheated and eventually cause permanent damage.

I have now devised an apparatus capable of avoiding such problems which is characterized by a recessed terminal box (i.e., where the terminal section of the control box is recessed or extended the desired distance into the resistance wire housing unit) which is installed in the duct. As a result, the resistance coil terminals and associated features such as the heat limiters and automatic reset thermal cutout, etc. are recessed into the airstream of the air duct thus furnishing the terminals with an airflow vital to proper operation.

The invention will be clearly evident from the present detailed description of the preferred embodiments and the drawings in which:

FIG. 1 is a perspective view of a conventional slip-in-type heater.

FIG. 2 is a perspective view of a flange" heater form of the invention showing how it is flanged joined to two flanged ducts.

FIG. 3 is an elevational view of a conventional heater of the prior art without a recessed terminal box with a cutaway of the control box to show the terminals therein.

FIG. 3A is an end view of the control box of FIG. 3, showing the terminals.

FIG. 4 is an elevational view of a typical heater of the present invention having a recessed terminal box with a cutaway of the terminal box showing the terminals in the recessed terminal box.

FIG. 4A is an end view of the control box of FIG. 4 showing the tenninals which are recessed.

FIG. 5 is an enlarged perspective view of a resistance wire terminal.

Electrical duct heaters are well known and illustrated in FIGS. 1, 2 and 3A. Except for FIG. 2, these are conventional heaters.

In general, the conventional heating devices of FIGS. 1, 3, and 3A comprise the following:

I. A resistance wire housing unit which contains:

1. the frame housing 2. a series of cross supports attached to the frame housing 3. resistance wire heating elements aligned within the housing frame and supported by the cross supports.

4. bushings which insulate resistance wires from the cross supports.

II. The control box which generally contains:

1. resistance wire terminals 2. auxiliary electrical control and supply features which may include some, or all, of the following features, plus others:

a. main electrical connections b. fuses c. magnetic contactors d. transformers e. control terminals f. automatic reset thermal cutout (as a primary safety protection when heater does not have sufficient airflow), etc.

g. manually resettable thermal cutouts or manually replaceable thermal cutouts (heat limiters) as secondary safety protection h. pneumatic electric switches i. fused or nonfused disconnects j. pilot lights k. pilot switches l. automatic or nonautomatic circuit breakers m. other features.

Thus, in conventional heaters there are two general housing units: v

l. The resistance wire housing unit which when installed fits into the duct.

2. The control box, attached to the resistance wire housing unit, which is installed outside the air duct.

The present invention in essence contains a true terminal box, (separate and distinct from the control box) containing the resistance wire terminals and related equipment which when installed is positioned within the duct. The remainder of the control box (i.e. which is not recessed into the ducts) is in essence the true control box (as distinguished from a separate 'terminal box) or a separated terminal section of the control box.

Resistance wire terminals are to be distinguished from field wiring and control terminals usually present in the control box.

A conventional prior art electric duct heater is illustrated in FIG. 1 which is called a slip-in heater, comprising the resistance wire housing unit and the control box. The resistance wire housing unit contains electric resistance coils strung at intervals within the body thereof through insulated holes in the cross support of resistance wire housing unit. The housing unit is installed totally within the duct. The control box, which contains electrical connections and optional auxiliary electrical equipment, is installed outside the duct. A second conventional prior art type of electric duct heater is called the flange" heater which has the basic structure and function of the slip-in heater except that instead of being inserted into the duct through a hole joins two flanged ducts by means of any suitable attaching means such as screws, nuts and bolts, etc. The relationship of heater assembly housing to control box is essentially the same in both cases. The numerals in FIGS. 1 and 2 have the same meanings as in FIGS. 3 and 4. In addition, the flanges are indicated by numeral 10.

FIG. 3 illustrates a conventional duct heater of the prior art wherein l is the resistance wire housing unit frame. The cross supports 2 are attached at right angles to the sides of the frame. The coiled resistance wires 3 are strung through insulated holes 4 in the cross supports. It is to be particularly noted that in the prior an embodiment, the resistance terminals 5 are positioned, when installed, in the control box 8 which is outside of the duct and is thus deprived of air circulation of the duct. The number and length of coils, cross supports, insulated holes, etc. will vary with the size and capacity of the particular heater. As can be seen from the end view of thehe heater of FIGS. 3 and 4 when the control box cover 8' is removed, each particular embodiment has terminals 5 with the corresponding lengths of resistance coils in the resistance wire housing unit. l-leat limiters are designated by 5' and the dotted lines 9 indicate the duct works.

FIG. 5 is an enlarged perspective view of a resistance wire terminal.

The duct heater of the present invention is illustrated in FIGS. 2, 4 and 4A. The critical difference between the present invention (illustrated in FIGS. 2, 4 and 4A) and the prior art embodiment (illustrated in FIGS. 3 and 3A) is the precessed terminal box 11 which is recessed the desired distance (which will vary with the particular unit) into the heating assembly so that the terminals are within the airflow of the duct and receive the benefit of such airflow and are now outside the air duct as is true in FIG. 3, the embodiment of the prior art. An end view of the control box of FIG. 3 is shown in FIG. 3A, and the end view of the recessed control box of FIG. 4 is FIG. 4A, with the essential difference being that in FIG. 4 the resistance wire terminals being recessed are positioned within the duct. In FIG. 2, the invention is shown applied to a flange-type duct heater and FIGS. 4 and 4A illustrate application of the invention to a slip-in"-type duct heater.

The primary safety automatic reset thermal cutout 7 having its terminal at 7' or the secondary safety manually resettable or replaceable thermal cutouts such as heat limiters 5' are also subject to premature tripping due to lack of adequate airflow near the resistance wire terminals.

In addition to the automatic reset thermal cutout (which is employed as primary safety protection) the resistance wire therminal box generally contains heat limiters and/or manually resettable thermal cutouts as secondary safety protection. Examples of heat limiters are fusible links set at a higher temperature than the automatic reset thermal cutout. Both the automatic reset thermal cutout and heat limiters or manual reset thermal cutouts are generally present in the recessed therminal box of commercial embodiments of the present invention.

The electrical connections and circuit diagrams are not presented in detail since they are conventional and well described in the literature.

In essence, the present invention has a true terminal box, as

distinguished from a control box, which terminal box is positioned within the air duct. he remaining part of the box is a true control box which is positioned outside the air duct. Generally, these two boxes are open to each other but may be closed to each other, if so desired. Thus, the present invention may be looked upon as a recessed terminal box which recesses the resistance wire terminals into the duct leaving the controls outside the duct, or as two distinct boxes-a true terminal box recessed into the duct and a control box positioned outside the duct.

Althoughthe invention has been described by making detailed reference to a currently preferred embodiment, this detail should be understood solely in an instructive, rather than in a limiting sense, numerous variations being contemplated as within the scope and spirit of this invention.

Having thus described my invention what I claim as new and desire to obtain by Letters Patent is I. A space heater adapted for use in a duct work system which heater contains a unitary assembly of l. a resistance wire housing unit including a frame housing supporting atleast one resistance wire heating element having a pair of terminals;

2. A control box attached to and positioned outside the resistance wire housing unit, and

3. a terminal box which contains the resistance wire terminals electrically connected to the controls of the control box; said terminal box being enclosed and attached to and adjacent to the control box and positioned within the resistance wire housing unit; said resistance wire housing unit, said terminal box and said control box being so dimensioned relative to the duct work system that when the space heater is installed within the duct work system both the resistance wire housing unit and the terminal box are recessed within the duct work system while the control box 15 outside the duct work system; said recessed terminal box containing thermal cutouts operatively connected to the heating element. 2. The space heater of claim which is the slip-in type. 3. The space heater of claim I which is the flange type. 

1. A space heater adapted for use in a duct work system which heater contains a unitary assembly of
 1. a resistance wire housing unit including a frame housing supporting at least one resistance wire heating element having a pair of terminals;
 2. A control box attached to and positioned outside the resistance wire housing unit, and
 3. a terminal box which contains the resistance wire terminals electrically connected to the controls of the control box; said terminal box being enclosed and attached to and adjacent to the control box and positioned within the resistance wire housing unit; said resistance wire housing unit, said terminal box and said control box being so dimensioned relative to the duct work system that when the space heater is installed within the duct work system both the resistance wire housing unit and the terminal box are recessed within the duct work system while the control box is outside the duct work system; said recessed terminal box containing thermal cutouts operatively connected to the heating element.
 2. A control box attached to and positioned outside the resistance wire housing unit, and
 2. The space heater of claim 1 which is the slip-in type.
 3. The space heater of claim 1 which is the flange type.
 3. a terminal box which contains the resistance wire terminals electrically connected to the controls of the control box; said terminal box being enclosed and attached to and adjacent to the control box and positioned within the resistance wire housing unit; said resistance wire housing unit, said terminal box and said control box being so dimensioned relative to the duct work system that when the space heater is installed within the duct work system both the resistance wire housing unit and the terminal box are recessed within the duct work system while the control box is outside the duct work system; said recessed terminal box containing thermal cutouts operatively connected to the heating element. 